For the sponge cake omelet, whisk egg yolks with 2 tablespoons sugar, vanilla sugar, lemon zest and a pinch of salt until foamy. For the snow, beat egg whites with granulated sugar until stiff and gently mix into the yolk mixture and stir in flour.
Heat a little butter or clarified butter in two omelet pans, pour a quarter of the mixture into each and bake in the preheated oven at 190°C for about 6 minutes. Turn out the omelettes, spread half of them with jam, fold them up and sprinkle them lightly with sugar. Bake the remaining omelettes in the same way.